Standards are set by the American Society of Mechanical Engineers (ASME) with regard to boilers and pressure vessels to ensure the safe and effective practice of boiler and pressure vessel manufacture and operation. These standards are set forth in the ASME Boiler and Pressure Vessel Code (hereinafter “the Code”), which indicates that calibration standards shall be of the same nominal diameter and thickness and the same nominal heat treatment condition as the piping and tubing used in the manufacture of pressure vessels being examined. The Code also indicates that calibration reflectors used in the testing shall be axial notches or grooves placed on the outside and inside surfaces of the calibration standard. The lengths, widths, and depths, of such notches or grooves are explicitly set forth in the Code and carefully controlled, as are distances between the notches or grooves.
Thus, a calibration standard for a particular heavy wall pipe material to be used in the construction of a boiler comprises a suitable length and configuration of the particular heavy wall pipe. The notches or grooves are used to calibrate non-destructive testing equipment that typically employ ultrasonic techniques. Such ultrasonic techniques generally assess the qualities of welds and determine pipe wall thicknesses as well as detect corrosion. In using ultrasound, ultrasonic pulse-waves at frequencies of up to about 50 MHz are applied to the pipe material at the notches placed therein. The particular topography (e.g., square, U-shaped, V-shaped) of the notch into which the pulse-waves are applied determines an expected return waveform. The return waveform is analyzed, and any deviation from the expected return waveform is assessed with regard to defects in the tested material.
In boiler construction, the pipes used can be sizable. Once located in the supplier market place, such pipes are typically sent to a suitable facility for notching and testing. The
notching may be performed using electrical discharge machining (EDM). In the process of EDM, a machine tool holds a shaped electrode which is advanced into the material to be tested to produce a shaped cavity (e.g., the notch). Power is supplied such that a high frequency series of electrical spark discharges are produced from the shaped electrode. Because the devices used in EDM are typically larger and heavier than samples of the pipes to be tested, samples of the pipes are brought to the EDM devices. Particularly when the pipes are very large (e.g., about 20 inches in diameter), the costs to transport the pipes from the market place, to the notching facility, to the testing facility, and to the site at which the pipes are to be used can be expensive.